1. Field of the Invention:
The present invention relates to a chromium additive for producing chromium alloys, and to a method for producing chromium alloys by use of the chromium additive.
2. Description of the Background:
Chromium has been used as an additive in various metallic materials, since chromium, as an alloying element, remarkably improves the heat resistance, corrosion resistance, and abrasion resistance of the alloy.
In recent years, in order to meet the increasing requirement for metals of higher performance characteristics, the quantity of chromium added to such metals has tended to increase.
In the past, ferrochrome has been almost exclusively used as a chromium additive (hereinafter referred to as an "additive") in the production of various chromium alloys, while metallic chromium prepared through the thermit process has been used as an additive for alloys such as chromium-aluminum alloys which do not require iron as an alloy constituent. However, ferrochrome contains iron in amounts as high as about 60% by weight, and also contains much carbon resulting from the use of carbon as a reducing agent in its production. On the other hand, metallic chromium prepared by the thermit process, although it is satisfactory from the viewpoint of chromium content, varies significantly in its quality because it is normally produced by a batch reaction, and additionally contains significant amounts of aluminum resulting from the use of aluminum as a reducing agent in its production.
Generally, superalloys which contain chromium as a main constituent are used in the manufacture of the likes of turbine blades which are employed in jet engines, oil pipes for deep oil wells, etc. Such applications require the addition of large amounts of chromium to a metal.
The use of ferrochrome or thermit metallic chromium as an additive in superalloys, as mentioned above, causes an adverse effect on properties of the superalloys because of the accompanying large contamination of the superalloys with carbon or aluminum.
The use of electrolytic metallic chromium, which contains lesser amounts of impurities, may be thought of as reasonable as an additive in such superalloys. However, electrolytic chromium has several disadvantages which include the fact that its production requires many steps and that the electrolytic chromium does not easily dissolve in the molten metal during the production of the alloys. A need therefore continues to exist for an improved method of adding chromium to various metals.